Variable reactance transformer



June 5, 1951 R J. A. ANDERSON 2,555,911

5 VARIABLE REACTANCE TRANSFORMER Filed Aug. 11, 1949 Fig. 2.

James A. Anderson INVENTOR.

BY MMF% I Patented June 5, 1951 UNITED STATES PATENT ()FFICE VARIABLEREACTANCE TRANSFORMER James A. Anderson, Memphis, Tenn.

Application August 11, 1949, Serial No. 109,738

Claims.

This invention relates to transformers provided with a control of thevoltage ratio between the primary and the secondary of the transformerand it has for its general object to provide a variable reactancetransformer of a simple and efficient type which is adjustable over awide range of variation and which is usable in connection with highamperage currents, such as used for welding equipment or for otherequipment supplying circuits with heavy and variable loads.

It is a further object of the invention to provide a variable reactancetransformer in which the reactance component of the transformer isadjustable at a uniform rate by means of a leakage path which is inparallel to but does not include the cores of the secondary or primarycoils of the transformer.

It is a further object of the invention to provide a variable reactancetransformer of the above mentioned type in which the variation of theinduction in the secondary coil is produced by a closed transformerframe connectible with a leakage path of variable magnetic reluctancewhich may be finely adjusted at a uniform rate by means of members whichare in contact with the closed transformer frame over variable crosssections.

It is a further object of the invention to provide a variable reactancetransformer of the above mentioned type in which a leakage path ofvariable magnetic reluctance is produced by means of a member which isin slidable contact with the two sides of a closed transformer frame,the area of contacts between the leakage path member and the transformerbeing made adjustable by a relative displacement of the aforesaidmembers.

It is a further object of the invention to provide a variable reactancetransformer of the above mentioned type in which a leakage path ofvariable magnetic reluctance is formed by means of a secondary core orleakage path member which is movable relatively to the closedtransformer frame containing cores for the primary and'secondary coilsand which is adapted to divert a portion of the magnetic flux generatedin the primary coil through contact surfaces of variable extension andthrough air gaps of variable width.

A further object of the invention consists in providing a variablereactance transformer of the above mentioned type which is of simple andefficient construction and in which an adjustable member providing aleakage path of variable magnetic reluctance is movably mounted on thetransformer frame and is moved towards and away from said frame bysimple mechanical means, such as a threaded spindle, said member beingin permanent sliding contact with the transformer frame during suchadjustment during which the magnetic reluctance of the leakage path ischanged by air gaps of variable width and by the change of the extensionof the contact surfaces through which the magnetic flux passes from thetransformer to the adjustable member, the permanent contact between thetransformer and said member during the change of the width of the gapspreventing the appearance of a vibration due to strong magnetic forcesacting across the gap.

Further and more specific objects of the in vention will be apparentfrom the following detailed specification.

The invention is illustrated in the accompanying drawing showing oneembodiment thereof by way of example. It is however to be understoodthat the example shown has been selected in order to explain theprinciple of the invention and the best mode of applying said principle.Other modes of applying the principle will be obvious to persons skilledin this art. It will therefore be clear that modifications of theexample shown in the drawing are not necessarily departures from theessence of the invention.

In the drawing:

Figure 1 is a diagrammatic elevational view of a transformer accordingto the invention.

Figure 2 is a diagram showing the two main parts of the arrangement inan extreme position.

For welding transformers and for similar transformers carrying heavyload currents and requiring an adjustable voltage and a high reactancein the load circuit variable transformers.

have been proposed regulating the voltage in the secondary or loadcircuit by adjusting the transformer reactance. Such variable reactancetransformers may be considered as a combination between a transformerand a reactor and the reactor part of the transformer with one type oftransformer consists in a magnetic path of variable reluctance arrangedin parallel to the main magnetic path passing through the primary andsecondary coil of the transformer. This parallel path usually includes amagnetic core located in the interior of the secondary coil. Thevariable reluctance of the magnetic path is customarily obtained byinserting into the same an air gap of adjustable width, this gap beingpref-- erably located in the magnetic core inside the secondary coil.This construction has been widely used in connection with transformersthe reactance of which is only adjusted occasionally to suit certainpermanently prevailing conditions. However this construction is muchless suitable for equipment which has to be adjusted during operation.The reason why this construction could not be adapted in a satisfactorymanner to variable reactance transformers in which frequent adjustmentsare to be made during operation resides in difficulties connected withthe adjustable air gap the movable member of which, under the heavymagnetic forces produced in connection with heavy amperages, could notbe protected against vibrations which lead to noise and to an earlydestruction of the movable member and of the gap adjustment mechanism.

According to the present invention the difliculties connected with thisearlier construction are overcome by the special construction of thetransformer. The main characteristic features of the constructionaccording to the invention consists in the use of a magnetic shuntcircuit or leakage path to be used in connection with a closedtransformer frame, which does not include a core of the primary orsecondary coil but which is established solely between the yokes joiningthe cores of the primary and secondary and adjacent portions and,further, in a special shunt circuit member which is provided withtapering leg members, adapted to slide along the yokes and to con tactthem to a variable extent, said member being further provided withshoulders adapted to be brought into contact with and to be removed fromthe yoke portion of the transformer frame.

The magnetic flux through the leakage path is therefore finely regulableby adjusting the pos'ition of the shunt circuit member and, as part ofthe said magnetic fiux always passes through surfaces which are indirect contact with each other, the difficulties resulting from themounting of adjustable members under a heavy variable magnetic stressare avoided. Moreover the structure is greatly simplified as the closedtransformer frame is not only the basic structure from which themagnetic flux branches off and is shifted to a secondary path but servesalso as a mechanical guide and holder for said branch or leakage pathmembers.

As seen from the figures the adjustable transformer, generally indicatedat 5, comprises a closed transformer core or frame 5 consisting of twocores 1, 8 and two yokes 9J9 joining them and forming a closed frame inthe well known manner. This structure may be laminated as usual.

The cores and 8 carry the primary coil Hi and the secondary coil l lrespectively. The coils are only indicated diagrammatically in thefigures but are much larger than indicated in the drawings.

Cooperating with the main transformer structure is the movable secondaryor leakage path member l2 which is so arranged that it bridges or shuntsthe frame 6.

The secondary member which forms a magnetic leakage path essentiallyconsists of an auxiliary core or bridge piece l5, provided with two legsl6, l8 projecting at right angles from the said auxiliary core or bridgepiece, which legs are so spaced that their inner surfaces are arrangedat a distance which is equal to the distance between the outer surfacesof the yokes 9 and I9. Therefore, said inner surfaces are adapted toslide along the outer surfaces the yoke members 3 and IQ of thetransformer frame 6.

The legs [6, l8 have ends 20 tapering off in one direction in such amanner that the cross section of the leg member which, in those portionswhich are close to the auxiliary core or bridge piece [5 issubstantially equal to the cross section of said piece, slowly decreasesin said end piece so that.

the ends are approximately linear.

At the junction of the auxiliary core or bridge piece [5 of the leakagepath member l2 and the leg members l6, l8 shoulders 2|, 22 are providedwith flux carrying surfaces at right angles to the inner surface of theleg members and parallel to the outer surface of the core 7 of thetransformer frame 6. These shoulders may be applied against the frame 6on both sides of the primary coil I0 Which'fits into the space betweenthe two shoulders 2|, 22 when the shunt member [2 is in its extremeposition in which there is full contact with the frame 6. When saidleakage path member [2 has been moved to this extreme position in whichcontacts between the frame 6 and the member I 2 has been established tothe fullest possible extent a portion of the magnetic flux which hasbeen produced in the core 1 by the primary coil IQ of the transformerand which would otherwise pass through core 8 and yokes 9, I9 isdeflected to the leakage path around the core l formed by the member 22which is now in contact with it along the shoulders 2|, 22 and along theinner sides of the end portion 20 of the legs I6, It.

In order to adjust the leakage path member l2 the transformer framecarries bars 2d, 25 which are riveted or bolted or otherwise secured tothe frame 6 and which are joined by a cross piece 26. The cross piecescarries a spindle 30 provided with screw threads which is rotatablymounted within said cross piece in any suitable manner. The spindle isprovided with a crank 21 from which a handle 28 projects. The spindlepasses through a bore 3| in the member l2, which member also carries asleeve 29 provided with inner screw threads engaging the screw threadsof the spindle 30.

It will thus be clear that a movement of the crank 21' entailing amovement of the spindle 30 will produce a movement of the leakage pathmember l2 towards and away from the frame 6 according to the directionin which the spindle has been rotated. Each such movement eitherincreases or decreases the extent to which the surfaces of the legmembers l6, H3 are in contact with the yokes 9, H3. Likewise, thedistance between the shoulders 2 I, 22 and the sides of the yokes offrame 6 is increased or decreased with the movement of the spindle.Obviously the magnetic flux through the leakage path decreases when themember I 2 is moved away from the frame 5. When full contact has beenmade along the entire inner surface of the leg members and along theiradjoining surfaces of the shoulders 2 I, 22 a considerable portion ofthe magnetic flux produced in the core i will pass through the leakagemember [2 thus influencing the inductive transmission from the primarycoil to the secondary coil l l, as the magnetic flux generated by theprimary coil in the core 1 will be practically divided into two pathswhich may or may If the leakage path member I2 is gradually moved awayfrom the transformer frame 6 the surfaces through which the leakagepath. is closed decrease gradually and the resistance of the gap betweenthe shoulders 21, 22 and the frame 6 increases. Thereby the distributionof the magnetic flux over the two paths is changed and the reluctance inthe shunt or leakage path circuit is increased. As a consequence themagnetic flux which passes to the secondary core increases and thevoltage in the load circuit increases proportionately.

It is seen that the above described construction disposes of many of thedisadvantages which are inherent in the customary constructions usingadjustable leakage paths. The member l2 which forms the leakage path isalways firmly held not only by the screw but by the magnetic forcesthemselves so that these forces assist in producing a stableconstruction and cannot pr duce vibrations. The air gaps which are usedare auxiliary gaps and therefore do not interfere with the operation orcause vibrations as in the customary constructions. It will also beobserved that there is always a direct contact between the yokes 9, I9and the legs l6, 18 through which the magnetic flux may pass while thegaps are widening. In the extreme position shown in Figure 2 in whichthe legs only touch the transformer frame 6 with their extreme linearends, the gap between the shoulders and the transformer frame has becomeso wide that no vibration can be produced. Moreover the member I2 isguided and held by the frame 6 and by the magnetic forces which have tobe overcome during adjustment and these forces increase and decrease sogradually during an adjustment that the adjusting operation can becarried out without difficulty.

It will be clear that changes of an unessential nature which are made inthe construction shown in the drawing will not affect the essence of theinvention.

Having described the claimed as new is:

1. A variable reactance transformer, comprising a closed transformerframe including cores and yokes joining said cores, a primary and asecondary coil mounted on said cores, a movable member including anadjustable auxiliary core piece adapted to form a magnetic shuntprovided with contact surfaces sliding on said closed transformer frameon both sides of the aforesaid coils to a variable extent and means foradjusting the area of contact of the contact surfaces of the saidmovable magnetic shunt memher with the closed transformer frame.

2. A variable reactance transformer, comprising a closed transformerframe including cores and yokes joining said cores, a primary and asecondary coil mounted on said cores, a movable leakage path memberincluding an auxiliary core piece arranged in substantial parallelismwith the cores of the closed transformer frame and provided with legmembers provided with inner contact surfaces in sliding contact with theyokes of the transformer frame at opposite sides thereof, and means foradjusting the position of said movable leakage path member with respectto the transformer frame.

invention, what is 3. A variable reactance transformer, comprising aclosed transformer frame including cores and yokes joining said cores, aprimary and a secondary coil mounted on said cores, a movable leakagepath member, including an auxiliary core piece, arranged in substantialparallelism with the cores of the closed transformer frame and providedwith leg members projecting at right angles to the said core piece fromthe same, said leg members having tapering ends and inner slidingcontact surfaces in contact with the yokes of the transformer frame atopposite sides thereof and means for adjusting the position of the saidmovable leakage path member with respect to the transformer frame, thusvarying the length of the contact surfaces on the legs in contact withthe said frame.

4. A variable reactance transformer, comprising a closed transformerframe including cores and yokes joining said cores, a primary and asecondary coil mounted on said cores, a movable leakage path memberincluding an auxiliary core piece, arranged in substantial parallelismwith the cores of the closed transformer frame and provided with legmembers projecting at right angles to the said core piece from the same,shoulder pieces arranged at the junction of the leg members with thecore, said leg members having tapering ends and inner contact surfacesin sliding contact with the yokes of the transformer frame and saidshoulder pieces having surfaces adapted to be applied against thetransformer frame on opposite sides of a coil carried by the core of theframe, and means for adjusting the position of the said movable leakagepath member with respect to the transformer core, thus varying thelength of the contact surfaces in active contact with the transformerframe and the gaps between said shoulder pieces and the said frame.

5. A variable reactance transformer, comprising a closed transformerframe including cores and yokes joining said cores, a primary and asecondary coil mounted on said cores, an auxiliary core piece forestablishing a leakage path around the cores of the transformer frame,means carried by said auxiliary core piece for maintaining activemagnetic contact of said core piece with two sides of the transformerframe along contact surfaces, further means carried by the saidauxiliary core piece to produce an air gap traversed by the magneticflux between said transformer core and said auxiliary core, and meansfor varying the area of the contact surface while simultaneously varyingthe width of the air gaps traversed by the magnetic flux.

JAMES A. ANDERSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,206,856 Shearer July 2, 19402,437,021 Fries Mar. 2, 1948 FOREIGN PATENTS Number Country Date 693,943France Nov. 26, 1930

